復合主鍵和多對一休眠

Question

我正在學習 Hibernate，並且正在嘗試使映射工作。 我的實體如下

部門：

@Entity
public class Department {

    @Id
    @GeneratedValue
    private Integer id;
    private String name;
    private String hqLocation;
    // getters and setters omitted for brevity 
}

工人編號：

@Embeddable
public class WorkerId implements Serializable {

    private Integer workerId;
    private Integer deptId;
    // getters and setters omitted for brevity 
}

工人：

@Entity
public class Worker {

    @EmbeddedId
    private WorkerId id;
    private String name;
    private Integer age;

    // How to make @ManyToOne mapping work?
    private Department department;
    // getters and setters omitted for brevity 
}

問題：如何使@ManyToOne on field private Department department; 工作？ 只需添加注釋結果private Department department; 作為null 。

Answer 1

真正的問題是，哪個實體應該是關系的所有者？ 你想映射雙向還是單向？

這是雙向示例

@OneToMany(
      fetch = FetchType.EAGER,
      mappedBy = "department",
      orphanRemoval = true,
      cascade = CascadeType.ALL)
private List<Worker> workers;


@JoinColumn(name = "department_id", nullable = false)
@ManyToOne(targetEntity = Department.class, fetch = FetchType.LAZY)
private Department department;

獲取類型是可選的，取決於用例

Answer 2

我認為您想使用“派生身份”； 所以你應該像這樣制作Worker.department ：

@Entity
public class Worker {

    @EmbeddedId
    private WorkerId id;
    private String name;
    private Integer age;

    @MapsId("deptId")
    private Department department;
    // getters and setters omitted for brevity 
}

JPA 2.2 規范的第 2.4.1 節討論了派生的身份（帶有示例）。